This invention relates to an induction system for an internal combustion engine and more particularly to an induction system that improves running characteristics at idle and low-speed without adversely affecting maximum speed performance of the engine.
It is known that internal combustion engines, particularly those which are called upon to run over a wide range of speed and loads such as an automotive application, have a tendency to run poorly at idle or low-load condition, unless extreme sacrifices are made in high-speed performance. It is also known that the results of this poor performance at light loads is due in large part to the slow-flame speed in the combustion chamber, which results among other things from the low-speed of the intake charge through the engine induction system. It has been proposed to improve slow-speed and idle operation of an engine by providing an auxiliary induction passage through which a substantial portion of the idle and low-speed charge requirements of the engine are provided. This arrangement insures high velocity of the charge entering the combustion chamber and, accordingly, rapid flame propagation and better running under these conditions. This arrangement has been found to both reduce the emissions of unwanted exhaust gas constituents while at the same time permitting an improvement in the fuel economy of the engine under these conditions. In some instances it may also be desirable to direct the sub-intake inlet in such a way so as to establish a swirl in the combustion chamber which is maintained during the compression stroke. Several embodiments of induction systems constructed in accordance with this concept are shown in the copending application for U.S. Letters Patent of Hiromitsu Matsumoto, entitled Control of Carburetor Supplied Induction System, Ser. No. 838,353, filed Sept. 30, 1977 and assigned to the assignee of this invention.
Although the induction systems shown in that patent application significantly improve the low-speed and idle operation of an engine without sacrificing emission control or fuel economy and, in fact, while improving these characteristics, it has been found that in some instances there is a tendency for the engine to run overly lean under idle and off-idle conditions, particularly at low temperatures. This leanness results from the condensation of fuel in the main intake passage at the time the throttle valve which diverts the flow through the auxiliary induction passage is closed.
It is, therefore, a principal object of this invention to provide an improved induction system for an internal combustion engine.
It is another object of the invention to provide an internal combustion engine induction system in which performance under all running conditions is improved.
It is a further object of this invention to provide an induction system for an internal combustion engine including an auxiliary intake system wherein the affects of fuel condensation at low temperatures are minimized.